A so-called bottle can member 1 which is formed by a drawing operation for a metal bottle member has a thread section 3 on a mouth section 2 and an outer periphery on an aperture section of the bottle can member 1 which is formed in a cylindrical shape which has a bottom section as shown in FIG. 6A. A product such as a drink water are filled in the bottle can member from the thread section 3. After that, an outer periphery of a cap 5 is compressed in accordance with the thread section 3. By doing this, the cap 5 is put thereon as shown in FIG. 6B. The cap 5 comprises a cap main upper section 6 to which a cap thread section 7 is formed in accordance with the thread section 3 of the bottle can member 1 and a cap main bottom section 9 which is formed on a bottom end of the cap main upper section 6 so as to expand over the bottom section of an expanding section 4.
Also, before the cap 5 is put has a shape like a cap member 5′ as shown in FIG. 6C such that an upper section is ceiled by a ceiling plate and its bottom section has an aperture section orthogonally in a downward direction so as to be a cylindrical shape. A score 8a which is formed in a plurality of cutting sections which are formed in a circumferential direction and a bridge 8b are disposed alternatively in a bridge section 8 such that the cap main body bottom section 9 is connected via the bridge section 8.
In order to remove the cap 5 from the bottle can member 1, a relative rotative force is applied to the cap 5 and the bottle can member 1. Such a rotative force serves such that the cap 5 should be moved upwardly by the thread section 3. However, the cap main body bottoms section 9 is engaged to an expanding section 4 of the bottle can member 1; therefore, the bridge 8b is broken; thus, the cap main body upper section 6 and the cap main body bottom section 9 are separated. Consequently, the cap main body bottom section 9 remains in the mouth section 2; thus, the cap main body upper section 6 is removed from the bottle can member 1. That is, the cap is opened on the bottle can member 1 by rotating the cap 5 by a user such that the bridge section 8 should be broken.
Conventionally, in the bottle can member 1 which has such a thread section 3, a diameter of an aperture section of a bottomed cylindrical bottle can member 1 as shown in FIG. 7A is reduced temporarily as shown in FIG. 7B. After that, as shown in FIG. 7C, a predetermined distance from the aperture end of the mouth section 2 is enlarged so as to form an enlarged diameter section 2′. Furthermore, as shown in FIG. 7D, a thread section 3 is formed in a constant distance from the aperture end such that an enlarged diameter section in which the thread section 3 is not formed remains for an expanding section 4; thus, the expanding section 4 is formed.
For an outer diameter A of the cap 5 which is put on the bottle can member 1 as shown in FIGS. 6A to 6C, there are three standards such as 28 mm, 33 mm, and 38 mm. An outer diameter B of the mouth section 1 of the bottle can member 1 is formed so as to be smaller than the outer diameter A of the cap 5. If the cap 5 which has 38 mm outer diameter is put to the thread section 3, the thread section 3 is formed so as to have an effective thread turn number approximately 1.5 to 1.7. The effective thread turn number is defined as a number of turns that are formed at a portion where the thread functions effectively.
Here, the effective thread turn number represents the number of thread turns that are formed at an effective thread section which is shown as X in FIG. 8. FIG. 8 is a view for explaining an over view for the thread section 3 in which Y and Z are incomplete thread sections. W indicates a perfect thread section. C indicates a center point. The thread section 3 is formed by a mountain section 3a and a valley section 3b. The incomplete thread section Y is formed in a starting side of an upper end of the mouth section 2. The incomplete thread section Z is formed an ending side of a base end side of the mouth section 2. Outer diameters for the mountain section 3a and the valley section 3b for a perfect thread section W between the incomplete thread section Y and the incomplete thread section Z are formed in predetermined diameters respectively. The diameter of the peak of the thread of the incomplete thread section Y increases gradually from an end point Y1 toward a starting point W1 of the perfect thread section W. The diameter of the valley of the thread of the incomplete thread section Z increases gradually from an end point W2 of the perfect thread section W toward the end point Z2.
The effective thread section X corresponds to a section starting at an effective thread start point X1, which is in a middle of the incomplete thread section Y, containing the entire portion of the perfect thread section W, and ending at an effective thread end point X2, which is in a middle of the incomplete thread section Z. The effective thread start point X1 is a cross point which is made by a bisector L1 which divides an acute angle ∠α for an incomplete thread section Y which is formed by an end point Y1, a center point C, and a starting point W1 and an incomplete thread section Y. An effective thread end point X2 is a cross point which is formed by a bisector L2 for an acute angle ∠β for the incomplete thread section Z which is formed by an end point W2, a center point C, and an end point Z2.
However, in a conventional bottle can member 1, if the effective thread turn number in the thread section 3 which is disposed in the mouth section 2 of the bottle can member 1 is approximately 1.5 to 1.7, a section in which there are two threads which are disposed toward a tip section from a base end section of the mouth section 2 and a section in which there is only one thread occur; thus, such a difference of the threads causes a problem. That is, if the thread turn number is formed as explained above, if a cap 5 is put on the bottle can member 1 such that a pressure in the bottle should be positive, a force is applied which pushes up the cap 5. A force for engaging the cap 5 is weak in a section in which there is only a thread; therefore, the cap 5 is disposed undesirably upwardly. That is, the cap 5 is disposed partially to the bottle can member 1; thus, a bridge 8b is strained in a section in which there is only a thread; thus, the thread is broken. That is, there has been a problem in that a bridge is broken. Also, the thread section 3 is compressed when the cap is put thereon more greatly than in a case in which there are more threads. Therefore, unequal sealing capability occurs in a circumferential direction; thus, there is a concern that there is a reduced airtight condition.
For resolving such a problem, there is a proposal for increasing the effective thread turn number. However, in a step for putting a cap 5 on the bottle can member 1, if a diameter of the cap is approximately 28 mm, the cap is pressed on the bottle by approximately 900 N force so as to wind up the cap therearound. However, if the diameter of the cap is 33 mm or greater, the force in the bottle for pushing up the cap is so great that a greater area for operating a molding operation is necessary. Therefore, the cap is compressed toward a ceiling surface of the bottle can at 1050 to 1200 N force by using a pressure block so as to wind up the cap therearound.
For example, if the effective thread turn number is 2.5 to 3, there are a section in which there are two threads and a section in which there are three threads. Therefore, in a step for molding a cap thread section 7 which is explained above, the section in which there are three threads may be deformed more easily than the section in which there are two threads. In such a case, a relative position between the position for compressing the cap by a thread forming roller and a position of a starting point W1 in a complete thread section W is shifted in an axial direction undesirably; thus, there is a section in which a thread is formed insufficiently. Also, a force is generated for raising a bottom section near a side section of the cap 5 in a axial line direction upwardly; thus, a bridge may be broken more easily if there are more threads. Therefore, if there is a section in which there are three threads, a bridge is broken more easily. In addition, after completing the winding operation for the cap, a pressure block is released. A section in which there are three threads serves as a spring so as to push up the cap. Therefore, a bridge near a section in which there are three threads may be broken more easily than a section in which there are two threads. Also, if the thread turn number is 3 or greater, a torque for opening a cap increases and a number for winding the cap also increases. Therefore, a user have to take more time and efforts for opening a cap accordingly; thus, such a case is not preferable.
If there is not a case in which a bridge is broken in a cap 5 due to an inner pressure of the bottle, an interval therebetween extends if the interval between the cap thread section 7 of the cap 5 and a ceiling surface is long; thus, there is a problem that a contact of the cap decreases. Also, if an interval between the cap thread section 7 of the cap 5 and the ceiling surface is narrow, the mouth section 2 cannot endure a force in a step for compressing the cap 5 thereon; thus, the mouth section 2 may be deformed undesirably.
Also, in a conventional technique, a bottle can which is commonly used for a can for a beverage is produced by a drawing operation by drawing a metal plate which is made of an aluminum and an aluminum alloy and an ironing operation which is supposed to be performed consequently. Such a can is called a DI can commonly. A mouth section is formed on an upper section of the DI can. After filling a content in such a bottle can, a cap is put on the mouth section of the bottle can; thus, a capped bottle can is produced.
Conventionally, a capped bottle can 101 which is shown in FIG. 11 is closed in an airtight manner by putting the cap 103 on the bottle can 102. A male thread section 105, an expanding section 106, and a curl section 107 are formed on the mouth section 104 which is disposed in the bottle can 102. The ceiling surface section 108, a female thread section 109, a pilfer proof section 110, and a bridge section 111 are formed in the cap 103 such that a liner 112 which is a sealing member is applied on an inner surface of the ceiling surface section 108. The cap 103 is attached to the bottle can 102 such that the male thread section 105 of the bottle can 102 and the female thread section 109 fit together and the bottom end section of the pilfer proof section 110 expands over the expanding section 106; thus, the cap 103 is sealed while the curl section 107 and the liner 112 contacts tightly. Also, the capped bottle can 101 has a structure so as to endure a predetermined inner pressure in case that the content thereinside is a carbonated beverage.
In order to open the capped bottle can 101, when the cap 103 is rotated with reference to the bottle can 102, the female thread section 109 is guided by the male thread section 105 so as to be moved upwardly. A bridge section 111 is cut by engaging the expanding section 106 and the pilfer proof section 110; thus, the curl section 107 and the liner 112 are separated. Furthermore, the cap 103 is removed from the bottle can 102 by rotating the cap 103. In such a case, when the cap 103 is rotated for opening the cap 103, a knurl section 113 is formed on the cap 103. The knurl section 113 is formed in an upper section of the female thread section 109 such that concave sections are formed periodically on protruding sections which have arc cross section which are disposed in a circumferential direction.
Also, in a step for winding the cap 103 on the bottle can 102, a cap member on which the female thread section 109 and the pilfer proof section 110 are not formed is applied on the bottle can 102. While a force is applied in a direction in which the cap member is compressed to the bottle can 102, the female thread section 109 and the pilfer proof section 110 are formed along the shape of the male thread section of the bottle can 102 and the shape of the expanding section 106. The curl section 7 and the liner 112 contacts more desirably by winding up the cap 3 while applying a force; thus, a more desirable sealing condition can be realized. In such a case, the effective thread turn number for male thread section and the female thread section 109 is formed to be approximately 1.5 to 1.7.
By the way, in the bottle can 102 to which the above cap 103 is put, if a pressure which is lower than a predetermined inner pressure is applied to the ceiling surface section 108 on the cap 103 and an interval between the female thread section 109 on the cap 103 and the ceiling surface section 108 is long, the interval extends: thus, there is a problem in that a contact between the curl section 107 and the liner 112 may be reduced. Also, a knurl section 113 is formed between the female thread section 109 on the cap 103 and the ceiling surface section 108; thus, there is a problem that the interval extends further.
Also, in order to solve such problems, it is possible to propose an idea in which an interval between the female thread section 109 on the cap 103 and the ceiling surface section 108 should be narrowed; that is, an interval from the male thread section 105 on the bottle can 102 to the upper end surface of the curl section 107 should be maintained in a low position. In such a case, there is a problem in that it bends undesirably because of insufficient rigidity against the pressing force to the cap 103 in a step for putting the cap 103.
Also, the effective thread turn number of the male thread section 105 is approximately to be 1.5 to 1.7; thus, there is a section in which there is a thread and there is a section in which there are two threads from the base end section of the mouth section 104 toward the tip section. Thus, there is a problem in that an engaging force in the male thread section 105 and an engaging force in the female thread section 109 are not constant over a circumferential direction of the mouth section 104. Because of this, even if the inner pressure in the bottle can 102 to which the cap 103 is put is at a predetermined inner pressure or lower, the cap 103 is shifted upwardly undesirably in a section in which there is a thread of which engaging force is weak; thus, there is a problem in that the contact between the curl section 107 and the liner 112 is reduced. Also, if the effective thread turn number is increased to be 2.5 or more so as to enhance the engaging force, there is a problem in that a torque for opening the cap needs to be greater.
Furthermore, in a conventional technique, in a so called bottle can member, a mouth section is formed in an aperture section of the bottle can member which has a bottomed cylindrical shape and a thread section is formed such that the cap should be put around an outer periphery of the mouth section.
In order to produce a bottle can member which has such a thread section, a bottle can member which has a bottomed cylindrical shape is produced in advance. As shown in FIG. 19A, a diameter of the aperture section of the bottle can member is reduced once so as to form a mouth section 202. After that, the diameter is enlarged by a predetermined distance from an end of the aperture end of the mouth section 202 so as to form an enlarged diameter section 202′ as shown in FIG. 19B. After that, a thread section 203 is formed at a predetermined distance from the aperture end by a thread forming device as shown in FIG. 19C. In such a case, when the thread section 203 is formed in the mouth section 202, an expanding section 204 is formed by maintaining a diameter enlarged section in which a thread section 203 is not formed.
In the conventional thread forming device, although it is not shown in the drawings, an inner core which contacts an inner surface of the mouth section 202 and an outer core which contacts an outer surface of the mouth section 202 rotate around an axial center of the bottle can member 201 while sandwiching the mouth section 2 with each other; thus, the thread section 203 is formed around an outer surface of the mouth section 202. In such a case, the thread turn number of the thread section 203 which is formed on the mouth section 202 is approximately 1.7 as shown in FIG. 19C.
Also, after that, in the bottle can member 201 on which the thread section 203 is formed, a tip of the mouth section 202 is bent from thereoutside to thereinside. After various steps for putting the cap for forming the curl section 208 as shown in FIG. 20, a content is filled thereinside; thus, the cap 205 is put shown in the drawing so as to seal there.
As explained above, in the conventional thread forming device, an inner core which contacts an inner surface of the mouth section 202 of the bottle can member 201 and an outer core which contacts an outer surface of the mouth section 202 rotate around an axial center of the bottle can member while sandwiching therebetween; thus the thread section 203 is formed which has a thread turn number 1.7 in the mouth section 202 of which diameter is enlarged.
However, if the thread turn number of the thread section is approximately 1.7, as shown in FIG. 20, there is a problem in that there is a section in which there two tread sections 203 on an peripheral surface of the mouth section 202 and there is a section in which there is only one thread section 203; thus, such a difference between the thread sections causes a problem. That is, if there is thread turn number which is explained above, if a pressure in the bottle can member 201 is positive when the cap 205 is put on the bottle can member 201, a pressure which pushes up the cap 205 is applied there; thus, the cap 205 is shifted upwardly undesirably. Therefore, the cap 205 is disposed partially with reference to the bottle can member 201; thus, a bridge 207 which is disposed between scores 206, 206 near the aperture end of the cap 205 is strained and broken. Thus, there is a problem in that there is a so-called a broken bridge.
In order to solve the above problems, it is tried to form a thread turn number 2.2 as shown in FIG. 21 by increasing the thread turn number of the thread section 203. When the thread section 203 which has 2.2 thread turn number on the mouth section 202 of the bottle can member 1 in this way, there is a thread section in which there are a first stage of the thread 203a, a second stage of the thread 203b, and a third stage of the thread 203c for the thread section 203 between the starting section 203A of the thread section 203 and the end section 203B.
By the way, when the thread section 203 which has 2.2 thread turn number is formed on the bottle can member 201 which has a thread area which has the above three threads, after that, a curl section 208 is formed for forming the curl section 208 on a tip of the mouth section 202 in a step for putting the cap while compressing the tip of the mouth section 202 by a cap putting device in a direction which is disposed toward the bottom of the bottle can member.
However, in such a case, the thread section 203 which has three thread sections is disposed; thus, a distance from the first stage of the thread 203a to the curl section 208 is close. Therefore, in a step for putting the cap, the first stage of the thread 203a of the thread section 203 is crushed because it is compressed downwardly by a compressing force by the cap putting device. Therefore, as shown in FIG. 22, a diameter of the first stage of the thread 203a is enlarged in a radial direction such that the first stage of the thread 203a protrude by Δ from a height of the second stage of the thread 203b and the third stage of the thread 203c in a circumference direction undesirably.
If the first stage of the thread 203a of the mouth section 202 is protruding in a circumferential direction ad the cap 20 is put on the bottle can member 201 consequently, the cap 205 is put thereon according to a shape of the mouth section 202; therefore, as shown in FIG. 22, a diameter of the aperture of the cap 205 is smaller than the outer diameter of a bottle thread 203a. Here, the cap 5 is shown in FIG. 22 under condition that a part of the cap 5 is broken.
The cap 205 which is put thereon under the above explained condition is removed from the bottle can member 201 such that the user can use it for drinking a content therein. Also, the mouth section 202 can be screwed so as to seal the mouth section when the user stops drinking the content therein. However, if the diameter of the end of the aperture of the cap is smaller than the diameter near the ceiling, a resistance between the mouth section 202 and the cap 205 is so great that a larger torque for closing the cap is necessary. Thus, there is a problem in that it is sometimes hard for handling it.